EDIT: (03/29/18) On yesterday's patch, this was finally fixed.
★ This was the note from the patch notes.....
► Fixed the "-40% health from healers" penalty on The Fists of Steel (it wasn't active)
► http://www.teamfortress.com/post.php?id=38643
If you want to actually play with any of the weapons shown on this YouTube channel, check out one of our TF2 servers!
★ Custom Weapons | USA
► 192.223.26.28:27015
★ Custom Weapons x10 | USA
► 192.223.26.28:27016
★ Custom Weapons MvM | USA
► 192.223.26.28:27017
★ Custom Weapons Stop that Tank | USA
► 192.223.26.28:27018
★ Custom Weapons | EU
► 185.107.96.197:27015
★ Custom Weapons x10 | EU
► 185.107.96.197:27016
★ Custom Weapons MvM | EU
► 185.107.96.197:27017
★ Custom Weapons Stop that Tank | EU
► 185.107.96.197:27018
Fun Fact: The "-40% healing from healers on wearer" on the Fists of Steel.... doesn't actually work! Plus the "-40% maximum overheal on wearer" mostly works.
In this video, I show that the reduced healing doesn't work (which includes less health from Medigun healing, Crossbow bolts, Dispensers/payload carts, health packs, and Mad Milk). I tested all healing sources just to test if the "wording of the negative attribute" was in-correct.
BTW, I did check while playing on a Valve casual server. I did this recording while on my testing server, so the testing would be clean.